<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 复合选择器 */
        div.hello{
            color: red;
            font-size: 30px;
        }
        p#world{
            color: green;
            text-decoration: underline;
        }
        /* 组合选择器，也称为集体声明 */
        span,.abc,p#xxx{
            font-weight: bold;
            background: #ccc;
            color: red;
        }
        /*  嵌套选择器 */
        /* h3 span{ */
        /* h3 > span{ */
        h3 p span{
            font-size: 40px;
        }
    </style>
</head>
<body>
    <p class="hello">aaa</p>
    <div class="hello">bbb</div>
    <p id="xxx">ccc</p>
    <span>ddd</span>
    <div>eee</div>
    <p id="world">fff</p>
    <span>ggg</span>
    <h3>
        <span>hhh</span>
    </h3>
    <h3>
        <p>
            <span>uuu</span>
        </p>
    </h3>
    <h2 class="abc">iii</h2>
</body>
</html>